I don't believe treaties are viable. That's not to say that governments look upon the idea unfavorably... just as they'd be willing to limit nuclear weapons if

I don't believe treaties are viable. That's not to say that governments look upon the idea unfavorably... just as they'd be willing to limit nuclear weapons if the other country will also do so, they'd probably do as much about espionage. The trouble is that it's not an enforceable treaty. We can plainly see how many nukes the USSR has, and we can call them on it. Kruschev can't just say "Oh, that's not our nuke in a big silo in the middle of Siberia, it must be some rogue general's!". But if we catch spies, they can certainly claim that those spies aren't theirs. With the nukes, the Soviets would (in theory, don't believe this ever happened for real) either dismantle those weapons that were prohibited by the treaty, or we'd arm up ourselves in retaliation (since the treaty was broken). How do you do that with spies, if they don't back down? You've gutted your intelligence networks, it will take decades to get assets in Moscow once more.